Position forecasting apparatus and position detection apparatus

ABSTRACT

A position forecasting apparatus for forecasting a position at a predetermined time of a continuously operating moving body is provided with an estimation part that finds an estimated position state of the moving body at a time in the past before the predetermined time and a position forecasting part that forecasts the position of the moving body at the predetermined time based on the estimated position state of the moving body estimated by the estimation part.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is based on Japanese Patent Application No.2017-62065 filed on Mar. 28, 2017, the disclosure of which isincorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to an apparatus for forecasting positionthrough operation of a moving body, and an apparatus for detectingposition through operation of the moving body.

BACKGROUND OF THE INVENTION

Conventionally, a position detection apparatus that detects a positionof a moving body such as a servo motor or the like attached to a machinemoving part in a machine tool or the like by detecting changes in aphysical quantity caused by rotational movement or the like of themoving body has been used. Through the output from this positiondetection apparatus, the rotational movement or the like of the movingbody is continuously tracked, and by providing feedback to the movingbody, movement control of the moving body is accomplished.

As this kind of position detection apparatus, an apparatus that isprovided with a magnetic field generation part for generating a magneticfield and a magnetic detection apparatus is known. This magneticdetection apparatus, in general, is provided with a magnetic detectionelement, which detects an external magnetic field generated by themagnetic field generation part and outputs an analog signal indicating aphysical quantity that the magnetic field generation part has relativelymoved, and a calculation circuit, which can convert the analog signalinto a digital signal and compute the position of the moving body at thepresent time based on this digital signal. This magnetic detectionapparatus is configured as an integrated circuit in which the magneticdetection element and the calculation circuit are integrated on the samesemiconductor chip.

Movement control of the moving body is accomplished based on theposition information of the moving body at the present time computed inthe calculation circuit of this magnetic detection apparatus. However,delays can arise from the filtering process for the analog signal outputfrom the magnetic detection element, the process of converting theanalog signal into a digital signal, the filtering process for removingnoise included in this digital signal and the process of computing theposition of the moving body at the present time based on the digitalsignal. Consequently, particularly to precisely control movement of amoving body operating at high speed and to make up for the delay, amethod that forecasts the position of the moving body at a future timefrom the position information of the moving body and controls the movingbody on the basis of this forecasted value is adopted.

As a position detection apparatus capable of implementing this kind ofmethod, conventionally, a rotation detection apparatus that includes amagnetic sensor element that measures the magnetic field strength ofmagnets provided in a rotating body, an angle calculation means forcalculating the rotation angle of the magnets from the measured value ofthe magnetic sensor element, a storage means for storing the data of therotation angle output from the angle calculation means, a rotationalstate estimation means for estimating the rotational state throughstatistical processing of the contents stored in the storage means, anextrapolation processing means for forecasting later rotational anglesfrom the rotational state estimated by the rotational state estimationmeans, and an output means for calculating and outputting a rotationalangle based on the rotational angle forecast by the extrapolationprocessing means have been proposed. (see Patent Literature 1).

PRIOR ART Patent Literature

-   [PATENT LITERATURE 1] JP Laid-Open Patent Application No.    2008-116292.

SUMMARY OF THE INVENTION Problem to be Solved by the Invention

In the rotation detection apparatus disclosed in the above-describedPatent Literature 1, the angle at the present time is output with afixed sampling period by the magnetic sensor element, and is stored andaccumulated in the storage means. Furthermore, processing such as anaveraging filter or the like is accomplished on the past angle data thatreaches the angle data of the present time stored and accumulated in thestorage means, and an angle at a sampling time to be forecast (forecastangle) is found.

Predetermined noise is included in the angle data of the present timeoutput at a fixed sampling period by the magnetic sensor element. Whenthe forecast angle is found through a linear extrapolation process as inthe above-described Patent Literature 1 using angle data that includessuch noise, there is a problem in that the accuracy of the forecastangle decreases. As is clear from the forecasting model shown in FIG.14, the angle θ_(X) at a prescribed sampling time T_(X) and the angleθ_(X−1) at a sampling time T_(X−1) more in the past each includespredetermined noise (in FIG. 14, an arrow indicates the noise width),and when making a linear extrapolation forecast of a forecast angleθ_(X+1) at a sampling time T_(X+1) more in the future from thepredetermined time T_(X) using these items of angle data, the noiseincluded in the forecast angle θ_(X+1) is amplified more than the noiseincluded in the angles θ_(X) and θ_(X−1).

In addition, when trying to find a forecast angle through an averagingfilter process or the like using the above-described angle data, a groupdelay caused by such occurs, and it is necessary to set the samplingtime to be forecast further in the future. When the sampling time to beforecast is set further in the future, it is impossible to control noiseamplification, creating the problem that the accuracy of the forecastangle decreases.

To increase the accuracy of the forecast angle, it is conceivable toprocess by a filter circuit or the like the angle data output by themagnetic sensor element to reduce the noise included in the angle data.Through processing by a filter circuit or the like, it is possible toreduce the noise included in the angle data. However, more delays occurthrough processes by filter circuits or the like, so the sampling timeto be forecast must be set further in the future. When the sampling timeto be forecast is set further in the future in this manner, the noisereduced by the filter circuit or the like is again amplified andincluded in the forecast angle. Consequently, the accuracy of theforecast angle decreases.

In consideration of the above problem, it is an objective of the presentinvention to provide a position forecasting apparatus that can forecastthe position of a continuously operating moving body at a predeterminedtime with extremely high accuracy, and a position detection apparatusthat includes the position forecasting apparatus.

Means for Solving the Problem

In order to resolve the above problem, the present invention provides aposition forecasting apparatus for forecasting a position at apredetermined time of a continuously operating moving body, and theposition forecasting apparatus is provided with an estimation part thatfinds an estimated position state of the moving body at a first time,which is earlier than the predetermined time, and a position forecastingpart that forecasts the position of the moving body at the predeterminedtime based on the estimated position state of the moving body estimatedby the estimation part.

Preferably, the above-described position forecasting apparatus isfurther provided with a calculation processing part that calculates theposition state of the moving body based on signals relating to theposition of the moving body output from a detection part, which detectsan external magnetic field of a magnetic field generation part providedin the moving body, and a simulation part, which finds a simulatedposition state of the moving body at the first time based on theestimated position state of the moving body at a second time, which ismore in the past than the first time, wherein the estimated positionstate of the moving body at the second time is estimated by theestimation part, and wherein the estimation part fmds the estimatedposition state of the moving body at the first time based on thesimulated position state found by the simulation part and the positionstate of the moving body at the first time calculated by the calculationprocessing part.

In the above-described position forecasting apparatus, preferably theposition state of the moving body at the first time is the positionstate at the latest of the position states of the moving body calculatedby the calculation processing part.

In the above-described forecasting apparatus, preferably the moving bodyis a rotationally moving body that rotates about a prescribed axis ofrotation, and the estimation part fmds estimated values of therotational angle, angular speed and angular acceleration of the movingbody at the position estimation time as the estimated position state.

In addition, preferably the present invention provides a positiondetection apparatus having the above-described position forecastingapparatus and a detection part that is positioned facing a magneticfield generation part provided in the moving body and that can detectthe position of the moving body. In this position detection apparatus,preferably the detection part includes a magnetoresistive effectelement.

Efficacy of the Invention

With the present invention, it is possible to provide a positionforecasting apparatus that can forecast the position of a continuouslyoperating moving body at a predetermined time with extremely highaccuracy and a position detection apparatus that includes this positionforecasting apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing a schematic configuration of arotational angle detection apparatus according to an embodiment of thepresent invention.

FIG. 2 is a side view showing a schematic configuration of therotational angle detection apparatus according to the embodiment of thepresent invention.

FIG. 3 is a block diagram showing a schematic configuration of therotational angle detection apparatus according to the embodiment of thepresent invention.

FIG. 4 is a circuit diagram schematically showing a circuitconfiguration of a detection part in the embodiment of the presentinvention.

FIG. 5 is a perspective view showing a schematic configuration of an MRelement as a magnetic detection element in the embodiment of the presentinvention.

FIG. 6 is a graph showing noise in models of Example 1 and ComparisonExamples 1˜2.

FIG. 7 is a graph showing simulation results in Example 1.

FIG. 8 is a graph showing simulation results in Comparison Example 1.

FIG. 9 is a graph showing simulation results in Comparison Example 2.

FIG. 10 is a graph showing noise in models of Example 2 and ComparisonExamples 3˜4.

FIG. 11 is a graph showing simulation results in Example 2.

FIG. 12 is a graph showing simulation results in Comparison Example 3.

FIG. 13 is a graph showing simulation results in Comparison Example 4.

FIG. 14 is a graph for explaining that noise included in forecast valuesis amplified in a linear forecasting model that uses angle dataincluding noise.

DETAILED DESCRIPTION OF THE INVENTION

The preferred embodiment of the present invention will be described indetail with reference to the drawings. FIG. 1 is a perspective viewshowing a schematic configuration of a rotational angle detectionapparatus according to this embodiment, FIG. 2 is a side view showing aschematic configuration of the rotational angle detection apparatusaccording to this embodiment, FIG. 3 is a block diagram showing aschematic configuration of the rotational angle detection apparatusaccording to this embodiment, FIG. 4 is a circuit diagram schematicallyshowing a circuit configuration of a detection part in this embodiment,and FIG. 5 is a perspective view showing a schematic configuration of anMR element as a magnetic detection element in this embodiment.

As shown in FIG. 1 and FIG. 2, a rotational angle detection apparatus 1according to this embodiment includes a magnet 2 and a magneticdetection apparatus 3 arranged opposite to the magnet 2. The magnet 2 isfixed to one end in the radial direction of a shaft part 11 (forexample, a motor shaft or the like of a servo motor or the like) thatrotates continuously about a rotational axis C, and rotates about therotational axis C in conjunction with rotation of the shaft part 11.

The magnet 2 has an end surface 21, which is orthogonal to therotational axis C. The magnet 2 has an N pole 22 and an S pole 23, whichare arranged symmetrically about a virtual plane that includes therotational axis C. The magnet 2 is magnetized in a direction orthogonalto the rotational axis C (a direction toward the N pole 22 from the Spole 23 and orthogonal to the boundary between the N pole 22 and the Spole 23). The magnet 2 generates a magnetic field based on themagnetization possessed by the magnet 2.

The magnetic detection apparatus 3 is arranged to face the end face 21of the magnet 2, and detects the magnetic field from the magnet 2. Therotational angle detection apparatus 1 according to this embodiment candetect the rotational angle of the magnet 2, that is, the rotationalangle of the shaft part 11 that moves rotationally, based on the outputof the magnetic detection apparatus 3.

As shown in FIG. 3, the magnetic detection apparatus 3 has a detectionpart 31, an A/D (analog-digital) conversion part 32, a calculationprocessing part 33, a simulation part 34, an estimation part 35 and aforecasting part 36. The detection part 31 detects the magnetic field ofthe magnet 2 (see FIG. 1, FIG. 2). The A/D conversion part 32 convertsthe analog signal output from the detection part 31 into a digitalsignal. The calculation processing part 33 calculates the digital signaldigitally converted by the A/D conversion part 32, and calculates arotational angle θ. The simulation part 34 simulates the rotationalangle θ_(S) at a prescribed sampling time based on a rotational angleθ_(E), angular speed ω_(E) and angular acceleration α_(E) estimated bythe estimation part 35. The estimation part 35 estimates the rotationalangle θ_(E), the angular speed ω_(E) and the angular acceleration α_(E)at the prescribed sampling time based on the rotational angle θ_(S)simulated by the simulation part 34 and the most recent rotational angleθ out of the rotational angles θ calculated by the calculationprocessing part 33. The forecasting part 36 forecasts a rotational angleθ_(P) at the present sampling time based on the estimation results(rotational angle θ_(E), angular speed ω_(E) and angular accelerationα_(E)) from the estimation part 35. In this embodiment, a positionforecasting apparatus capable of forecasting the position (rotationalposition) of the continuously operating moving body (for example, themotor shaft or the like of a continuously rotating servo motor) isconfigured by at least the calculation processing part 33, thesimulation part 34, the estimation part 35 and the forecasting part 36.

As shown in FIG. 4, the detection part 31 includes a first detectionpart 31A and a second detection part 31B, and the first and seconddetection parts 31A and 31B each include at least one magnetic detectionelement. The detection part 31 generates and outputs detection signals(analog signals) relating to the angle (rotational angle) formed by thedirection of the magnetic field of the magnet 2 with respect to aprescribed direction, at a prescribed sampling period (one samplingperiod is around 50˜100 μsec, for example).

Each of the first and second detection parts 31A and 31B may include apair of magnetic detection elements connected in series as at least onemagnetic detection element. In this case, each of the first and seconddetection parts 31A and 31B has a Wheatstone bridge circuit thatincludes a first pair of magnetic detection elements connected inseries, and a second pair of magnetic detection elements connected inseries.

A Wheatstone bridge circuit 311 possessed by the first detection part31A includes a power source port V1, a ground port G1, two output portsE11 and E12, a first pair of magnetic detection elements R11 and R12connected in series, and a second pair of magnetic detection elementsR13 and R14 connected in series. One end of each of the magneticdetection elements R11 and R13 is connected to the power source port V1.The other end of the magnetic detection element R11 is connected to oneend of the magnetic detection element R12 and the output port E11. Theother end of the magnetic detection element R13 is connected to one endof the magnetic detection element R14 and the output port E12. The otherend of each of the magnetic detection elements R12 and R14 is connectedto the ground port G1. A power source voltage of a prescribed size isimpressed on the power source port V1, and the ground port G1 isconnected to ground.

A Wheatstone bridge circuit 312 possessed by the second detection part31B has the same composition as the Wheatstone bridge circuit 311 of thefirst detection part 31A, and includes a power source port V2, a groundport G2, two output ports E21 and E22, a first pair of magneticdetection elements R21 and R22 connected in series, and a second pair ofmagnetic detection elements R23 and R24 connected in series. One end ofeach of the magnetic detection elements R21 and R23 is connected to thepower source port V2. The other end of the magnetic detection elementR21 is connected to one end of the magnetic detection element R22 andthe output port E21. The other end of the magnetic detection element R23is connected to one end of the magnetic detection element R24 and theoutput port E22. The other end of each of the magnetic detectionelements R22 and R24 is connected to the ground port G2. A power sourcevoltage of a prescribed size is impressed on the power source port V2,and the ground port G2 is connected to ground.

In this embodiment, it is possible to use MR elements such as TMRelements, GMR elements or the like for all of the magnetic detectionelements R11˜R14 and R21˜R24 included in the Wheatstone bridge circuits311 and 312, and using TMR elements is particularly preferable. The TMRelements and the GMR elements have a magnetization fixed layer in whichthe magnetization direction is fixed, a free layer in which themagnetization direction changes in accordance with the direction of animpressed magnetic field, and a nonmagnetic layer arranged between themagnetization fixed layer and the free layer.

Specifically, as shown in FIG. 5, the MR element has a plurality ofbottom electrodes 41, a plurality of MR films 50 and a plurality of topelectrodes 42. The plurality of bottom electrodes 41 is provided on asubstrate (unillustrated). Each of the bottom electrodes 41 has a long,slender shape. A gap is formed between two bottom electrodes 41 adjacentin the lengthwise direction of the bottom electrodes 41. The MR films 50are respectively provided near both ends in the lengthwise direction onthe top surface of the bottom electrodes 41. The MR films each include afree layer 51, a nonmagnetic layer 52, a magnetization fixed layer 53and an antiferromagnetic layer 54, laminated in that order from thebottom electrode 41 side. The free layer 51 is electrically connected tothe bottom electrode 41. The antiferromagnetic layer 54 is configured byantiferromagnetic materials, and by causing exchange coupling with themagnetization fixed layer 53, serves the role of fixing the direction ofmagnetization of the magnetization fixed layer 53. The plurality of topelectrodes 42 is provided on the plurality of MR films 50. Each of thetop electrodes 42 has a long, slender shape, is arranged on two of thebottom electrodes 41 adjacent in the lengthwise direction of the bottomelectrodes 41, and electrically connects the antiferromagnetic layers 54of two adjacent MR films 50 each other. The MR films 50 may have aconfiguration in which the free layer 51, the nonmagnetic layer 52, themagnetization fixed layer 53 and the antiferromagnetic layer 54 arelaminated in that order from the top electrode 42 side. In addition, theantiferromagnetic layer 54 may be omitted by providing the magnetizationfixed layer 53 with a so-called Synthetic Ferri Pinned layer (SFP layer)having a laminated Ferri structure of ferromagnetic layer/nonmagneticintermediate layer/ferromagnetic layer in which the two ferromagneticlayers are antiferromagnetically coupled.

In TMR elements, the nonmagnetic layer 52 is a tunnel bather layer. InGMR elements, the nonmagnetic layer 52 is a nonmagnetic conductivelayer. In TMR elements and GMR elements, the resistance value changes inaccordance with the angle formed by the direction of the magnetizationof the free layer 51 with respect to the direction of magnetization ofthe magnetization fixed layer 53. The resistance value becomes a minimumwhen this angle is 0° (when the magnetization directions are mutuallyparallel), and the resistance value becomes a maximum when this angle is180° (when the magnetization directions are mutually antiparallel).

In FIG. 4, the directions of magnetization of the magnetization fixedlayers of the magnetic detection elements R11˜R14 and R21˜R24 areexpressed by filled-in arrows, and the directions of magnetization ofthe free layers are expressed by outlined arrows. In the first detectionpart 31A, the direction of magnetization of the magnetization fixedlayers of the magnetic detection elements R11 and R14 is a directionparallel to a first direction D1, and the direction of magnetization ofthe magnetization fixed layers of the magnetic detection elements R12and R13 is an antiparallel direction to the direction of magnetizationof the magnetization fixed layers of the magnetic detection elements R11and R14. In the first detection part 31A, the electric potentialdifference between the output ports E11 and E12 changes in accordancewith the strength of the component of the magnetic field of the magnetic2 in the first direction D1, and a signal expressing the strength of themagnetic field of the magnet 2 in the first direction D1 is output.

In the second detection part 31B, the direction of magnetization of themagnetization fixed layers of the magnetic detection elements R21 andR24 is a second direction D2 (a direction orthogonal to the firstdirection D1), and the direction of magnetization of the magnetizationfixed layers of the magnetic detection elements R22 and R23 is anantiparallel direction to the direction of magnetization of themagnetization fixed layers of the magnetic detection elements R21 andR24. In the second detection part 31B, the electric potential differencebetween the output ports E21 and E22 changes in accordance with thestrength of the component of the magnetic field of the magnetic 2 in thesecond direction D2, and a signal expressing the strength of themagnetic field of the magnet 2 in the second direction D2 is output.

A difference detector 37 outputs a signal corresponding to the electricpotential difference between the output ports E11 and E12 to the A/Dconversion part 32 as a first signal S1. A difference detector 38outputs a signal corresponding to the electric potential differencebetween the output ports E21 and E22 to the A/D conversion part 32 as asecond signal S2.

As shown in FIG. 4, the magnetization direction of the magnetizationfixed layers of the magnetic detection elements R11˜R14 in the firstdetection part 31A and the magnetization direction of the magnetizationfixed layers of the magnetic detection elements R21˜R24 in the seconddetection part 31B are orthogonal to each other. In this case, thewaveform of the first signal S1 becomes a cosine waveform dependent onthe rotational angle θ, and the waveform of the second signal S2 becomesa sine waveform dependent on the rotational angle θ. In this embodiment,the phase of the second signal S2 differs from the phase of the firstsignal S1 by ¼ of a signal period by, that is, π/2 (90°).

The A/D conversion part 32 converts the first and second signals (analogsignals related to the rotational angle θ) S1 and S2, output from thedetection part 31 with a prescribed sampling period, into digitalsignals, and these digital signals are input into the calculationprocessing part 33.

The calculation processing part 33 accomplishes calculation processingon the digital signals converted from analog signals by the A/Dconversion part 32, and calculates the rotational angle θ of the magnet2. This calculation processing part 33 is configured by a microcomputeror the like, for example. The rotational angle θ of the magnet 2calculated by the calculation processing part 33 is stored in a storagepart (unillustrated) included in the calculation processing part 33.

The rotational angle θ of the magnet 2 can be calculated through anarctangent calculation shown in the below equation, for example.

θ=atan(S1/S2)

Within a 360° range, there are 2 solutions of the rotational angle θ inthe above equation, differing by 180°. However, through the combinationof signs of the first signal S1 and the second signal S2, it is possibleto determine which of the two solutions to the above equation is thetrue value of the rotational angle θ. That is, when the first signal S1has a positive value, the rotational angle θ is larger than 0° andsmaller than 180°. When the first signal S1 has a negative value, therotational angle θ is larger than 180° and smaller than 360°. When thesecond signal S2 has a positive value, the rotational angle θ is withinthe range of 0° or more and less than 90° and larger than 270° and 360°or less. When the second signal S2 has a negative value, the rotationalangle θ is larger than 90° and smaller than 270°. The calculationprocessing part 33 calculates the rotational angle θ within the 360°range based on the determination of the combination of signs of thefirst signal S1 and the second signal S2.

The simulation part 34 simulates a rotational angle θ_(S) of the magnet2 at a prescribed sampling time from the rotational angle θ_(E), angularspeed ω_(E) and angular acceleration α_(E) of the magnet 2 at a pastsampling time estimated by the estimation part 35 and stored in thestorage part. For example, the simulation part 34 can simulate therotational angle θ_(S) of the magnet 2 at the prescribed sampling timeby, for example, accomplishing extrapolation processing or the likeabout the rotational angle θ_(E) of the magnet 2 at a past sampling timeestimated by the estimation part 35.

The estimation part 35 estimates the rotational angle θ_(E) of themagnet 2 at the prescribed sampling time and also estimates the angularspeed ω_(E) and the angular acceleration α_(E), by reflecting therotational angle θ of the magnet 2 at the prescribed sampling time onthe rotational angle θ_(S) of the magnet 2 found by the simulation part34.

The forecasting part 36 forecasts a rotational angle θ_(P) of the magnet2 at the present sampling time based on the rotational angle θ_(E), theangular speed ω_(E) and the angular acceleration α_(E) of the magnet 2estimated by the estimation part 35. For example, the forecasting part36 calculates the rotational angle θ_(P) of the magnet 2 at the presentsampling time by, for example, accomplishing extrapolation processing orthe like about the rotational angle θ_(E) or the like of the magnet 2estimated by the estimation part 35.

In the rotational angle detection apparatus 1 having the above-describedconfiguration, when the magnet 2 rotates accompanying rotation of theshaft part 11, the magnetic field of the magnet 2 changes. Theresistance values of the magnetic detection elements R11˜R14 and R21˜R24of the detection part 31 change in accordance with changes in thismagnetic field, and the signals S1 and S2 expressing the magnetic fieldstrength of the magnet 2 in the first direction D1 and the seconddirection D2 are output from the difference detectors 37 and 38 at aprescribed sampling period, in accordance with the electric potentialdifferences of the respective output ports E11, E12, E21 and E22 of thefirst detection part 31A and the second detection part 31B. Furthermore,the first signal S1 and the second signal S2 from the differencedetectors 37 and 38 are outputted and are converted into digital signalsby the A/D conversion part 32. Following this, the rotational angle θ ofthe magnet 2 is calculated by the calculation processing part 33.

In the rotational angle detection apparatus 1 according to thisembodiment, delays arise from the filtering process about analog signalsbased on output from the detection part 31, the process of converting todigital signals by the A/D conversion part 32, the filtering processabout the digital signals, the calculation process in the calculationprocessing part 33, and so forth. To make up for this delay, forecastingof the rotational angle by the forecasting part 36 becomes important.

For example, in the rotational angle detection apparatus 1 according tothis embodiment, a delay of three sampling times arises from the variousprocesses. Whereupon, at the present sampling time T_(n), the rotationalangle θ_(n−3) of the magnet 2 at the third sampling time T_(n−3) priorto the present sampling time T_(n) is output by the calculationprocessing part 33. On the other hand, the simulation part 34 simulatesand finds the rotational angle θ_(Sn−3) of the magnet at the thirdsampling timeT_(n−3) prior to the present sampling time T_(n), based onthe rotational angle θ_(En−4), the angular speed ω_(En−4) and theangular acceleration α_(En−4) of the magnet 2 at the fourth samplingtime T_(n−4) prior to the present sampling time T_(n), which areestimated by the estimation part 35, for example. The estimation part 35reflects the rotational angle θ_(n−3) of the magnet calculated by thecalculation processing part 33 (the most recent rotational angle of themagnet 2 at the present sampling time T_(n)) on the rotational angleθ_(Sn−3) of the magnet 2 simulated by the simulation part 34 andestimates the rotational angle θ_(En−3) of the magnet 2 at the thirdsampling time prior to T_(n−3) and also estimates the angular speedω_(En−3) and the angular acceleration α_(En−3). Furthermore, theforecasting part 36 forecasts the rotational angle θ_(Pn) of the magnet2 at the present sampling time T_(n) based on the rotational angleθ_(En−3), the angular speed ω_(En−3) and the angular accelerationα_(En−3) of the magnet 2 estimated by the estimation part 35.

Predetermined noise is included in the rotational angle θ of the magnetcalculated by the calculation processing part 33. When attempting toforecast the rotational angle θ_(Pn) at the present sampling time T_(n)based on the rotational angle θ that includes this noise, the noiseincluded in the forecast value of the rotational angle θ_(Pn) that wasforecasted is amplified, making correct forecasts difficult. Inaddition, in a forecasting method using the angular speed ω and theangular acceleration a previously proposed by this inventor (JapanesePatent Application 2015-67498), reduction of the noise included in theforecast rotational angle θ_(Pn) was possible, but there was apossibility that the forecast value of the rotational angle θ_(Pn) woulddeviate from the rotational angle θ calculated by the calculationprocessing part 33. In this forecast method, in a moving bodyrotationally moving at high speed, within an extremely short time (forexample, around 3 sampling periods or less prior to the present samplingtime T_(n)), the rotational movement of the magnet 2 is assumed to beconstant speed rotational movement or constant acceleration rotationalmovement. Thus, assuming that the angular speed ω_(n−3) and the angularacceleration α_(n−3) at the third prior sampling time T_(n)−3 and theangular speed ω_(n) and the angular acceleration α_(n) at the presentsampling time T_(n) can be assumed to be substantially the same, and byforecasting the rotational angle θ_(Pn) of the magnet 2 at the presentsampling time T_(n) based on the angular speed ω_(n−3) and the angularacceleration α_(n−3) calculated from the actually measured value of therotational angle θ_(n−3) of the magnet 2 at the third prior samplingtime T_(n−3) (the rotational angle θ_(n−3) calculated by the calculationprocessing part), it is possible to reduce the noise included in therotational angle θ_(Pn). However, the rotational angle θ_(n−3) at thethird prior sampling time T_(n−3) used in forecasting the rotationalangle θ_(Pn) of the magnet 2 at the present sampling time T_(n) is anactually measured value (rotational angle θ_(n−3) calculated by thecalculation processing part 33), so it is conjectured that the problemarises that the rotational angle θ_(Pn) forecast by the forecasting part36 will deviate from the actually measured value.

On this point, in this embodiment, the rotational angle θ_(En−3), theangular speed ω_(En−3) and the angular acceleration α_(En−3) at thethird prior sampling time T_(n−3) used in order to forecast therotational angle θ_(Pn) of the magnet 2 at the present sampling timeT_(n) are estimated values, so it is possible to resolve the problem ofthe rotational angle θ_(Pn) forecast by the forecasting part 36deviating from the rotational angle θ_(n) calculated by the calculationprocessing part 33, and it is possible to extremely accurately forecastthe rotational angle θ_(Pn) of the magnet 2 at the present sampling timeT_(n).

In this manner, the rotational angle θ_(Pn) of the magnet 2, which isforecasted with high accuracy by the forecasting part 36, is input intoa driver circuit or the like (unillustrated) of the moving bodyincluding the shaft part 11 (for example, a servo motor or the likeincluding a motor shaft), and movement control of the moving body isaccomplished. Accordingly, it is possible to accomplish movement controlof the moving body with high accuracy.

As described above, with the rotational angle detection apparatus 1according to this embodiment, the rotational angle θ_(En−3), the angularspeed ω_(En−3) and the angular acceleration α_(En−3) used in order toforecast the rotational angle θ_(Pn) at the present sampling time T_(n)by the forecasting part 36 are found by reflecting the rotational angleθ_(n−3) at the prior sampling time calculated by the calculationprocessing part 33 at the present sampling time T_(n) on the rotationalangle θ_(Sn−3) simulated by the simulation part 34, so it is possible toextremely accurately forecast the rotational angle θ_(Pn) at the presentsampling time T_(n) based on the rotational angle θ_(En−3), the angularspeed ω_(En−3) and the angular acceleration α_(En−3).

In addition, with the rotational angle detection apparatus 1 accordingto this embodiment, the rotational angle θ_(En−3), the angular speedω_(En−3) and the angular acceleration α_(En−3) estimated by theestimation part 35 in order to forecast the rotational angle θ_(Pn) ofthe magnet 2 at the present sampling time T_(n) are found only by usingthe most recent rotational angle θ_(n−3) calculated by the calculationprocessing part 33 and the rotational angle θ_(Sn−3) simulated by thesimulation part 34, so an effect is achieved that can reduce the volumeof information (number of samplings) necessary for forecasting therotational angle θ_(Pn).

The above-described embodiment was described to facilitate understandingof the present invention and is not intended to limit the presentinvention. Accordingly, each element disclosed in the above-describedembodiment should be construed to include all design modifications andequivalents belonging to the technical scope of the present invention.

In the above-described embodiment, an example in which the forecastingpart 36 forecasts the rotational angle θ_(Pn) at the present samplingtime T_(n), but this is intended to be illustrative and not limiting,and, for example, it would be fine to forecast the rotational angleθ_(Pn+3) in the future from the present sampling time T_(n) (forexample, the third sampling time ahead T_(n+3)).

In the above-described embodiment, the magnet 2 fixed to the shaft part11 was used as the magnetic field generation part, but this is intendedto be illustrative and not limiting For example, it would be fine to usea magnet in which at least one group of N electrodes and S electrodes ispositioned alternately in a ring shape as the magnetic field generationpart and to position the magnetism detection apparatus facing the outerperimeter of this magnet, and it would be fine to use a linear scale asthe magnetic field generation part.

In the above-described embodiment, the magnet 2 moves rotationallyrelative to the magnetic detection apparatus 3 by the shaft part 11 towhich the magnet 2 is fixed rotating about the rotational axis C, butthis is intended to be illustrative and not limiting. For example, themagnet 2 (shaft part 11) and the magnetic detection apparatus 3 mayrotate in mutually opposite directions, or the magnetism detectionapparatus 3 may rotate while the magnet 2 (shaft part 11) does notrotate.

EXAMPLES

Below, the present invention is described in greater detail by citingexamples, but the present invention is not limited in any way to thebelow-described examples.

Example 1

In relation to the forecast of the rotational angle θ_(Pn) at thepresent sampling time T_(n) by the forecasting part 36 in the magneticdetection apparatus 3 having the configuration shown in FIG. 3 and FIG.4, simulations were accomplished using MATLAB and noise included in theforecasted value of the rotational angle θ_(Pn) was found. In thesesimulations, it was assumed that the magnet 2 moves at a constantrotational speed of 10,000 deg/sec, the sampling period by the detectionpart 31 is 50 μsec, the noise included in the rotational angle θcalculated by the calculation processing part 33 is ±0.1 deg (see FIG.6), and a group delay of three sampling times (150 μsec) occurs. Inaddition, it was assumed that the simulation part 34 simulates therotational angle θ_(Sn−3) at the third prior sampling time T_(n−3)through extrapolation processing using the rotational angle θ_(En−4),the angular speed ω_(En−4) and the angular acceleration α_(En−4) at thefourth prior sampling time T_(n−4), the estimation part 35 estimates therotational angle θE_(n−3), the angular speed ω_(En−3) and the angularacceleration α_(En−3) by reflecting the rotational angle θ_(n−3) at thethird prior sampling time T_(n−3) on the rotational angle θ_(Sn−3), andthe forecasting part 36 forecasts the rotational angle θ_(Pn) through alinear extrapolation process using the estimated values of θ_(En−3),ω_(En−3) and α_(En−3). Simulation results are shown in FIG. 7.

Comparison Example 1

The noise included in the forecasted value of the rotational angleθ_(Pn) was found in the same manner as in Example 1 except that themeasurement was performed. The rotational angle θ_(Pn) at the presentsampling time T_(n) was forecasted by accomplishing a linearextrapolation process using the rotational angles θ_(n−3)˜θ_(n−5) atthree sampling times T_(n−3)˜T_(n−5) calculated by the calculationprocessing part 33. Simulation results are shown in FIG. 8.

Comparison Example 2

The noise included in the forecasted value of the rotational angleθ_(Pn) was found in the same manner as in Example 1 except that therotational angle θ_(Pn) at the present sampling time T_(n) wasforecasted by accomplishing a moving average filter process using theangular speeds ω_(n−3)˜ω_(n−6) that are respectively the firstderivative of the rotational angles θ_(n−3)˜θ_(n−6) at the four samplingtimes T_(n−3)˜T_(n−6). Simulation results are shown in FIG. 9.

As is clear from the results of Example 1, Comparison Example 1 andComparison Example 2 (see FIGS. 7˜9), it was confirmed that throughforecasts using the rotational angle θ_(En−3), the angular speedω_(En−3) and the angular acceleration α_(En−3) estimated by theestimation part 34, it is possible to extremely accurately forecast therotational angle θ_(Pn) at the present sampling time T_(n) withoutamplifying the noise, even if a predetermined amount of noise isincluded in the rotational angle θ.

Example 2

The noise included in the forecasted value of the rotational angleθ_(Pn) was found in the same manner as in Example 1. The magnet 2 wastaken to be rotationally moving with a constant acceleration of 2×10⁸deg/sec², and the noise included in the rotational angle θ calculated bythe calculation processing part 33 increased with larger speeds, asshown in FIG. 10. Results are shown in FIG. 11.

Comparison Example 3

The noise included in the forecasted value of the rotational angleθ_(Pn) was found in the same manner as in Example 2 except that therotational angle θ_(Pn) at the present sampling time T_(n) is forecastedby accomplishing a linear extrapolation process using the rotationalangles θ_(n−3)˜θ_(n−5) at the three sampling times T_(n−3)˜T_(n−5)calculated by the calculation processing part 33. The simulation resultsare shown in FIG. 12.

Comparison Example 4

The noise included in the forecasted value of the rotational angleθ_(Pn) was found in the same manner as in Example 2 except that therotational angle θ_(Pn) at the present sampling time T_(n) is forecastedby accomplishing a moving average filter process using the angularaccelerations α_(n−3)˜α_(n−6) that are respectively the secondderivative of the rotational angles θ_(n−3)˜θ_(n−6) at the four samplingtimes T_(n−3)˜T_(n−6). The simulation results are shown in FIG. 13.

As is clear from the results of Example 2, Comparison Example 3 andComparison Example 4 (see FIGS. 11˜13), it was confirmed that throughforecasts using the rotational angle θ_(En−3), the angular speedω_(En−3) and the angular acceleration α_(En−3) estimated by theestimation part 34, it is possible to extremely accurately forecastwithout amplifying the noise, even if a predetermined amount of noise isincluded in the rotational angle θ, and without the forecast value ofthe rotational angle θ_(Pn) at the present sampling time T_(n) deviatingfrom the true value (the rotational angle θ_(n) calculated by thecalculation processing part 33).

DESCRIPTION OF REFERENCE SYMBOLS

-   1 Rotational angle detection apparatus (position detection    apparatus)-   2 Magnet (magnetic field generation part)-   3 Magnetism detection apparatus-   31 Detection part-   33 Calculation processing part-   34 Simulation part-   35 Estimation part-   36 Forecasting part

1-6. (canceled)
 7. An apparatus for forecasting a state at apredetermined time of a continuously operating moving body, theapparatus comprising: an estimation part that finds an estimated stateof the moving body at a first time, which is earlier than thepredetermined time; a forecasting part that forecasts the state of themoving body at the predetermined time based on the estimated state ofthe moving body estimated by the estimation part; a calculationprocessing part that calculates the state of the moving body based onsignals relating to the state of the moving body output from a detectionpart that detects an external magnetic field of a magnetic fieldgeneration part provided in the moving body; and a simulation part thatfinds a simulated state of the moving body at the first time based onthe estimated state of the moving body at a second time, which is morein the past than the first time, wherein the estimated state of themoving body at the second time is estimated by the estimation part;wherein the estimation part finds the estimated state of the moving bodyat the first time based on the simulated state found by the simulationpart and the state of the moving body at the first time calculated bythe calculation processing part.
 8. The apparatus according to claim 7,wherein the state of the moving body at the first time is the state atthe latest of the states of the moving body calculated by thecalculation processing part.
 9. The apparatus according to claim 7,wherein: the moving body is a rotationally moving body that rotatesabout a predetermined axis of rotation; and the estimation part findsestimated values of the rotational angle, angular speed and angularacceleration of the moving body at the state estimation time as theestimated state.
 10. An apparatus for forecasting a state at apredetermined time of a continuously operating moving body, theapparatus comprising: an estimation part that finds an estimated stateof the moving body at a first time, which is earlier than thepredetermined time; a forecasting part that forecasts the state of themoving body at the predetermined time based on the estimated state ofthe moving body estimated by the estimation part; a calculationprocessing part that calculates the state of the moving body based onsignals relating to a physical quantity of the moving body; and asimulation part that finds a simulated state of the moving body at thefirst time based on the estimated state of the moving body at a secondtime, which is more in the past than the first time, wherein theestimated state of the moving body at the second time is estimated bythe estimation part; wherein the estimation part finds the estimatedstate of the moving body at the first time based on the simulated statefound by the simulation part and the state of the moving body at thefirst time calculated by the calculation processing part.
 11. A statedetection apparatus, comprising: the apparatus according to claim 7; anda detection part that is positioned to face a magnetic field generationpart provided on the moving body and that can detect the state of themoving body.
 12. The detection apparatus according to claim 11, whereinthe detection part includes a magnetoresistive effect element.